In a storage phosphor computed radiography imaging system as described in U.S. Pat. No. 31,847, reissued Mar. 12, 1985, to Luckey, a storage phosphor, also known as a stimulable phosphor, is exposed to an x-ray image of an object, such as the body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with relatively long wavelength stimulating radiation such as red or infrared light produced by a helium neon gas laser or diode laser. Upon stimulation, the storage phosphor releases emitted radiation of an intermediate wave-length, such as blue light, in proportion to the quantity of x-rays that were received. To produce a signal useful in electronic image processing the storage phosphor is scanned in a raster pattern by a laser beam deflected by an oscillating or rotating scanning mirror or hologon. The emitted radiation from the storage phosphor is reflected by a mirror light collector and detected by a photodetector such as a photomultiplier to produce an electronic image signal. Typically the storage phosphor is translated in a page scan direction past the laser beam which is repeatedly deflected in a line scan direction perpendicular to the page scan motion of the storage phosphor to form a scanning raster patter of a matrix of pixels.
The storage phosphor is then erased so that it can be reused again. Successful erasure results in removal of any residual image and any background image noise. Many techniques have been used to erase storage phosphors.
U.S. Pat. No. 4,496,838, issued Jan. 29, 1985, inventors Umemoto et al., discloses a noise erasing apparatus for a stimulable phosphor sheet having an erasing source of light having a wavelength range of 400 nm to 600 nm. The light source can be a fluorescent lamp, a laser source, a sodium lamp, a neon lamp, a metal halide lamp or an Xenon lamp.
U.S. Pat. No. 4,439,682, issued Mar. 27, 1984, inventors Matsumoro et al., discloses a noise erasing method including sequential first and second erasings. The first erasing is conducted to erase the radiation image previously stored in the storage phosphor. The second erasing is carried out just before the phosphor is to be used again, to erase fog which develops after the first erasing.
U.S. Pat. No. 5,065,021, issued Nov. 12, 1991, inventor Arakawa, U.S. Pat. No. 5,422,208, issued Jun. 6, 1995, inventors Kojima et al., and U.S. Pat. No. 5,550,386, issued Aug. 27, 1996, inventors Kojima et al., disclose erasing a stimulable phosphor sheet after image read out, by first exposing the storage phosphor to first erasing light having light of wavelengths within the ultraviolet range and then second exposing the storage phosphor to second erasing light having wavelengths longer than the ultraviolet range.
U.S. Pat. No. 5,665,976, issued Sep. 9, 1997, inventor Arakawa, discloses a storage phosphor erasing method including sequential exposure to a first erasing light which contains no light component of a wavelength range which can be detected by photoelectric readout means, as the storage phosphor is fed away from a read-out section and to a second erasing light which contains a light component in the wavelength range which can be detected by the photoelectric readout means, as the storage phosphor is fed back to the readout section.
U.S. Pat. No. 5,371,377, issued Dec. 6, 1994, inventors Struye et al., discloses a method of storage phosphor erase using light in the wavelength range of 370 nm to 530 nm containing two separate emission bands, one peaking at or near 400 nm (ultraviolet) and the other at or near 500 nm (blue/green).
U.S. Pat. No. 6,140,663, issued Oct. 31, 2000, inventors Neary et al., discloses a storage phosphor erase method using a first radiation source having a wavelength of 577 to 597 nm while preventing ultraviolet light-the source includes a yellow light emitting diode, and a second radiation source having wavelengths including at least one of infrared or near infrared.
EP Patent Publication No. 0 136 588 B1, granted May 15, 1991, inventors Hosoi et al., discloses a storage phosphor erase source includes a light emitting diode emitting light in the wavelength range of 728–850 nm.
See also: EP Patent Publication No. 0 182 095 B1, granted Jan. 4, 1989, inventors Kimura et al., Japanese Patent Provisional Publication Nos. 56 (1981)-11392, 58 (1982)-83839 and 59 (1984)-202099.
Despite the many techniques proposed for erasing a readout storage phosphor, there is a need for an erasure technique that is low in cost, does not use mercury, has long life, compact size, mechanical rigidity and is suitable for erase during scan.